Hydroxamic acids and their salts (hereinafter referred to as hydroxamates) are used in collection of minerals such as pyrochlore, muscovite, phosphorite, hematite, pyrolusite, rhodonite, rhodochrosite, chrysocolla, malachite, bornite, calcite, gold and other precious metals. Hydroxamates are particularly useful in froth flotation of copper minerals particularly oxidized copper minerals.
The hydroxamates used in collection of minerals generally comprise a hydrocarbyl group such as an aryl, an alkylaryl or a fatty aliphatic group. Hydroxamates may exist in a complex array of forms due to resonance conjugation such as the following: 
The presence of these forms and the relative concentrations may depend on the solvent, pH and presence of other compounds such as counter ions. Furthermore if restricted rotation about the C—N bond occurs then discrete Z and E isomers may also exist 
The structure of the hydroxamic acids in solution and the effect of isomerism on performance in froth flotation is not understood.
Processes have been described for the preparation of hydroxamates in the acid form. For example, Rothenberg U.S. Pat. No. 6,145,667 describes the preparation of hydroxamic acids as a solution in an oil or fatty alcohol. Our copending international application PCT/AU01/00920 describes preparations of fatty hydroxamates in the form of a solid salt such as the potassium or sodium salt. We have found that the use of the hydroxamate in an organic solvent or in acid or the dry form significantly reduces the activity of hydroxamate in froth flotation. We believe that this occurs as a result of a substantial portion of the acid or salt being present in an inactive form.